Electric circuit



May 1940 K. J. GERMESHAUSEN 2,201,166

ELECTRIC CIRCUIT Filed March 9, 1957 2 SheetsSheet l j11/v/7vo 7'flennetip J Gervneskcauseba y 1940. K. J. GERMESHAUSEN 2,201,166

ELECTRIC CIRCUIT Filed March 9, 1937 2 Sheets-Sheet 2 Patentd May 21,1'.

UNITED STATES PATENT OFFICE Application March 9, 1937, Serial No.129,837

35 Claims.

The present invention relates to electric circults, and moreparticularly to circuits particularly adapted for uses requiring largepeak currents, with relatively small average currents.

An object of the present invention is to provide a novel electriccircuit embodying a coldcathode gaseous-discharge device of thecharacter described in Letters Patent 2,185,183, granted January 2,1940, and application, Serial No. 129,- 838, filed March 9, 1937,particularly circuits requiring intermittent or occasional operation.The invention is of broad and general utility, such as for stroboscopicand relay purposes and power control.

Othercbjects will be explained hereinafter and will be particularlypointed out in the appended claims.

For a consideration of what I believe to be novel and my invention,attention is directed to the accompanying description and the claimsappended thereto.

In the accompanying drawings, Fig. 1 is a longitudinal section of apreferred gaseous-discharge tube that may be connected into circuit inaccordance with my invention; Fig. 2 is a simple stroboscope circuitembodying a discharge lamp of the above-described character with asingle control grid; Fig, 3 is a circuit embodying a lamp of theabove-described character with two grids; and Fig. 4 illustrates apreferredcomplete stroboscope circuit embodying the invention.

The tube employed in the circuits embodying the present invention may beof the type illustrated in the said Letters Patent, or a modification ofthe same, illustrated in Fig. 1 and described more at length in the saidcopending application, Serial No. 129,838. It comprises an evacuatedglass envelope l, filled with a suitable gas, such as neon, or any ofthe other noble gases, such as argon or helium. The pressure of the gasin the tube may vary, the usual pressure be ing from one to twocentimeters, The tube contains several electrodes, namely, a solidcathod 2, an anode or plate 5, and .one or more grids, inner and outergrids being shown at 3 and 4 between the anode and the cathode. Thesource of the electrons is a bright cathode spot on the surface of thecathode. Either grid may be used as the control grid, depending upon thepolarity and the magnitude of the control voltage.

As illustrated in Fig. l, the cathode may comprise a metal cup 33secured within and closing the lower end of a ceramic insulatingcylinder 32; In the cup is a. pill 8 that may be constituted of amixture of materials that can react chemically to produce a substance ofrelatively low work-function, and that do not combine chemically withthe gas in the envelope I. A

pill of compressed caesium chloride and aluminum filings or powderanswers to this description. The pill forms the active material of thecathode and is held in place by a wire-mesh screen 9. The cylinder 32prevents the discharge from forming on the outside of the cup.

The grids may also be supported by the insu- 10 lating cylinder 32. Tothis end, the cylinder 32 may be provided with an inwardly projectingflange 34, on the inner side of which is secured a metal cylinder whichserves as the grid 3. The other grid 4 comprises a carbon cylinder whichis secured to, or rests upon, the upper end of the cylinder 32. Thecylinder 4 is placed so that caesium does not sputter on its surface.

As explained in the said Letters Patent, the grid 3 may, in normal use,by placed close to the '20 cathode 2, say, not more than a fewmillimeters from the cathode, and may be of such shape that the cathodewill sputter a thin surface layer or coating of a material of lowwork-function, such as caesium, on the grid surface. A thin surfacecoating or layer of the caesium or other material of low work-functionis thus'maintained on the grid 3 during the normal operation of thetube. As illustrated in Fig. 1, however, and as explained in the saidapplication, Serial No. 129,838, the grid 3 may, under somecircumstances, be precoated.

The hereinafter-described cathode spot is more easily formed on the pillof caesium chloride and aluminum than on pure caesium. This is due tothe fact that thecaesium chloride and alumi num are in effect surfaceimpurities or irregularities. If the pill 8 were made of pure caesium,furthermore, or for other reasons furnished too much free caesium, or ifthe arc discharge between the cathode and the anode werenon-intermittent, the caesium would be quickly sputtered and evaporatedover the tube, and the cathode would have very short life.

Viewed from one aspect, therefore, the pill 8 is composed of a chemicalcompound of caesium which is slowly broken down under the action of thecathode spot, liberating free caesium. Viewed from another aspect, thepill is composed of a mixture of caesium with a material which retardsthe vaporization of the caesium under the action of the cathode spot.

Other materials than caesium chloride and aluminum may be used for thepill 8; for example, mixtures of caesium chloride and cadmium or zinc,and mixtures of caesium chloride and rubidium chloride and aluminum,cadmium or zinc. Other metals than caesium, such' as the alkali metals,the alkali-earth metals, or the rare-earth metals, may be used toprovide the active material of the cathode. Examples of these aremixtures of sodium chloride and lead; mixtures of barium chloride andaluminum or zinc; barium oxide; strontium oxide; and misch metal. Alltests have shown the caesium compounds to be most satisfactory.

In general, a chemical compound of one of the alkali, alkali-earth, orrare-earth, metals mixed with a metal which will displace the combinedmetal, or a mixture of one of the alkali, alkaliearth, or rare-earth,metals with a substance which will retard the vaporization of the metal,will be satisfactory and will provide a cathode on which the cathodespot may be readily formed. The action of the cathode spot should evolvea material of low work-function, so that advantage can be taken of theease of cathodespot formation on these materials.

The screen 9 facilitates .the formation of a cathode spot on the pill byproviding a number of points for the concentration, at the surface ofthe cathode, of the glow-discharge current from the anode which precedesthe arc discharge. Irregularities and impurities on the surface of thecathode also assist in concentrating and localizing the electrical glowdischarge on the cathode to produce the cathode spot on the cathode, andthereby render the electrical discharge an arc discharge. If the screen9 is omitted, the local current density at the cathode may not becomehigh enough to cause the formation of a cathode spot, and the dischargebetween the anode and the cathode would then hold over in a glowdischarge.

The form of the arc stream between the anode and the cathode is a columnof small diameter which has high intrinsic brilliance, withsubstantially all the light emitted from the concentrated arc stream.This discharge is easily distinguished from a glow discharge, whichoccupies substantially the whole interior of the tube, with a dischargeof low intrinsic brilliance, the greatest brilliance being at thesurface of the cathode.

The grids 3 and 4 and the cylinder 32 constitute a chimney or restrictedpassage for the arc discharge, rendering the voltage dropof the arcstream more constant and, therefore, increasing the stability of theoperation of the tube.

The cylinder 32, furthermore, overcomes some tendency for the dischargebetween the anode and the cathode to become a glow discharge between theoutside of the cathode and the anode. This tendency is further resistedby placing the active material of the cathode at the bottom of the cupor cylinder, since there is a greater tendency for a cathode spot toform on an inner surface. such as the bottom of a depression, or in acorner, than there is for the cathode spot to form on an outer surface.

The anode is so placed that caesium is not sputtered on its surfaceduring the operation of the tube. As an additional precaution, it alsomight be made of a material, such as carbon, to which the caesium doesnot readily adhere.

The advantages of tubes of the above-described character are veryclearly shown by their use as intermittent light sources in theillustrated circuits.

In the circuit of Fig. 2,, a tube I is illustrated having but a singlegrid 4'. The anode I and the cathode 2 of the tube are shown connectedacross a condenser I I, which is continuously charged, by

way of conducting wires 1 and 8, from a suitable direct-current source(not shown) of, say, 300 to 400 volts, connected through a variablecurrentlimiting impedance I2, which may be a resistor, or a combinationof resistance and inductance. The wire I is shown as the positiveconducting lead and the wire 8 as the negative lead. The source may beone or more batteries (not shown), direct-current generators (notshown), thermionic or gaseous-discharge rectifiers for producing directcurrent from alternating current, as illustrated in Fig. 4, or any othersource of direct current. The grid 4 is connected through a resistanceor other impedance 6' to the anode 5.

In'the operation of the circuit, the condenser I I starts to becomecharged from the direct-current source through the impedance I2, thetube being nonconductive. When the voltage across the condenser IIreaches the-required value, say 110 volts, however, the voltage betweenthe grid 4 and the cathode 2 exceeds the breakdown value and the tubebecomes conducting.

Because of the glow discharge thus formed between the grid and thecathode, an electrical discharge will start between the anode and thecathode through the gas in the envelope I. If the impedance in thecircuit comprising the condenser, the anode and the cathode is low, thecurrent will instantly rise to a value sufllcient to start a cathodespot. This results in a low-drop arc discharge in the tube, the currentrises to a very high value (say, 300 amperes) and the tube emits abrilliant flash of light. The low impedance of the discharge pathpermits the condenser to discharge almost instantly, the current andflash of light lasting a few microseconds. When the voltage across thecondenser has fallen to a value approximately equal to the arc drop, thetube current is maintained only by the flow through the chargingimpedance I2. The values of this impedance and of the direct-currentsupply must be such that the residual current is too small to maintainthe cathode spot. When this is the case, the tube drop must rise to thatnecessary to maintain a glow discharge, which is some ten times thatnecessary to maintain the arc. By the time the voltage of the condenserhas risen to this value, the tube has had time to extinguish and returnto its normal non-conducting state, and will remain so until the gridvoltage has again reached the value necessary to cause breakdown of thetube.

The arc through the tube II is not maintained. because of the action ofthe impedance I2, which limits the current flow to such an extent thatthe arc is extinguished. a

The fact that the condenser, together with the leads to the electrodesof the tube, forms an oscillatory circuit, further assists in theextinguishing of the tube, tending to cause the voltage across the tubeto fall to a value lower than the arc drop of the tube, or even, toreverse polarity.

The condenser II is thus periodically charged from the source of voltagesupply and then discharged through the tube I, from the anode to thecathode.

The impedance of the discharge circuit comprising the condenser I I andthe tube I should be sufficiently low so that the current will rise tothe value necessary to start the cathode spot (say, 5 amperes). Unlessthis is so, the circuit will not operate priiperly and the tube I mayhold over into a continuous glow discharge.

The current passes between the anode and the cathode continually butinterruptedly to set up continually discharges of are characteristicbetween the cathode and the anode. It is of amperage sufliciently highto produce a potential gradient on sin-relatively small area only of thecathode high enough to extract electrons from the cathode while thecathode remains cold," at low average temperature, and to produce a fallof cathode potential lower than that occurring in a glow discharge. Theaverage value of the said current is nevertheless relatively low. It issumciently low, indeed, so that its root-meansquare value, that is, theheating current, through the tube, is low enough so that the averagetemperature applied by the current to the cathode is less than thetemperature at which substantially incandescent cathode emission isproduced. The reaction takes place, therefore, at relatively lowtemperature, and is not progressive or explosive, and the cathode spotis formed on the cathode continually but interruptedly. The resuit isthat the layer of the material of low workfunction, such as caesium, iscontinually replaced during the operation of the tube. If the pill 8 isconstituted of caesium chloride and aluminum, as before described, forexample, the action of the cathode spot causes the caesium chloride tobreak down, aluminum being substituted for the caesium and formingaluminum chloride. In addition to the material of low-work functionproduced by the reaction of the cathode spot on the material of thecathode. there may be produced also various unwanted gaseous productswhich may be detrimental to the operation. If the material contains anoxide, for example, an unwanted gas may be oxygen. These unwanted gasesmay be absorbed by the aluminum or by magnesium. The intervals betweenthe discharges are sufllciently large so that the average temperature ofthe cathode remains low enough to prevent rapid disintegration of thecathode. If the heating current were great enough to cause the cathodeto become overheated, the reaction mixture in the cathode wouldcompletely react, and the caesium would all become displaced from itssalt, so as to become evaporated onto the surface of the bulb. Anapproximate value of root-mean-square current for a small tube is 50milliamperes.

If a blow discharge is maintained in the tube, the permissibleroot-mean-square current will be less than 50 milliamperes, since thecathode voltage drop is higher, and hence the heating efi'ect at thecathode will be greater for a given current.

The operation of the circuit described above is similar to that of thewell-known relaxation-oscillator circuit using a glow tube. Due,however, to the special tube employed, the circuit oscillates morereadily, without tending to hold into a steady glow, it can handle alarge average power, and it is capable of producing very large momentarycurrents. Typical values for the constants of the circuit in Fig, 2 mayhe as follows:

Supply voltage --volts D. C 400 Resistance l2 ohms 3000 Capacity llmicrofarads 4 Average current milliamperes 40 Maximum current in thetube amperes 300 The voltage at which the glow discharge from the gridto the cathode begins and that of the arc drop in the tube are so nearlyconstant that the light flashes from the tube occur at substantiallyconstant frequency. They may, therefore. be used forstroboscopicpurposes. Therate at which the flashes occur can becontrolled by changing the variable resistance II, the supply voltage,or the capacity II. The lamp is particularly adapted for use as astroboscope, be-

cause the moment that'the discharge stops, the illumination also stops.The glow does not persist and the cathode 2, being a cold cathode, gives011' no light itself, the light being produced by the discharge betweenthe cathode 2 and the anode 5. As the discharge between the cathode 2and the anode 5 is under the control or the grid 4, it is possible, bysuitably energizing and deenergizing the grid 4 at rapid intervals,therefore, to send discontinuous current surges rapidly through thevapor of the tube.

In Fig. 3, potentiometers l4 and it are shown connected across thecondenser II. The grid 3 is shown connected to a movable arm of thepotentiometer l4 through the resistor or other impedance III. Thismovable arm divides the potentiometer l4 into parts ill and 82, theformer of which is connected between the cathode 2 and the grid 3, andthe latter between the grid 3 and the plate 5. The grid 4 is connectedthrough a resistance IE to the movable arm of the potentiometer I B. Asthe resistance of the potentiometers is large, they require very littlecurrent. The last-named movable arm divides the potentiometer it intoparts 19 and 80, the former of which is connected between the cathode Iand the grid 4 and the latter between the grid 4 and the plate 5. Thecondenser II is thus connected to the impedances of the parts BI and 82of the potentiometer l4, connected in series. and to the impedances ofthe parts l9 and 00 of the potentiometer l6, likewise connected inseries. The potentiometers are normally set by the said movable arms sothat the grid 8 is positive with respect to the cathode 2 and the grid 4is positive with respect to the grid 3.

By properly setting the potentiometers, it is possible to have thevoltage between the anode 5 and the cathode 2 much greater than thevoltthem, and then transfers to the anode-cathode circuit.

The voltage applied between the grids 3 and 4 should be sufllcient tocause an initiating glow discharge between the cylinder 4 and thecoating on the cylinder 3. The voltage at which this discharge takesplace is low and substantially constant, due to the fact that the grids3 and 4 shield the field between the grids from charges on the glass.The grids 3 and 4 also provide a restricted passage for the arcdischarge, which results in substantially constant tube drop. The grid 3shields the cathode from the grid 4 so that changes in the surface ofthe cathode do not atfect the starting of the glow discharge between thegrids. To start the blow discharge between the grids may require avoltage of only about a hundred volts and a current of only a fractionof a milliampere, so very little power is required.

If desired, the flashing of the tube can be controlled by a contactori'l connected to the positive side of the condenser through a resistancetween the grids 3 and 4 to exceedthe breakdown voltage and'the tube'willbecome conducting.

Fig. 4 illustrates a complete stroboscope circuit, with a conventionalpower supply to furnish direct current from the'alternating-currentmains, a separate oscillator to drive the st'roboscopic lamp so as tocause the lamp to flash at the desired frequency, a means forcalibrating the oscillator. a means for operating the lamp so as tocause it to flash at the frequency of the alternating-currentsupply-voltage from the line, and a contactor device for controlling theflashing rate.

In this circuit, a transformer 18, a doubleanode rectifier tube 11 and acondenser 89 form a conventional power supply'to give any desireddirect-current voltage, say, 300 volts, from the 110-voltalternating-current mains. It isunderstood that any source of directcurrent of about 300 volts can be substituted for the power supplyshownin the drawings.

The stroboscope circuit of Fig. 4 is in many respects similar to that ofFig. 3. The impedances 19 and are, however, shown connected between thecathode 2 and the grid 4, and between the grid 4 and the'anode 5,respectively; the impedance 8| is shown connected between the cathode 2and the grid 3; and the impedance 82 is omitted, together with theimpedance I8 and the contactor I1; their function being performed byother elements, as will hereinafter appear. The'bias is so adjusted onthe grid 8 by means of these impedances, and the supply voltage is soadjusted, that it is possible to have the voltage between the anode 5and the cathode 2 much greater than the voltage required to cause a glowdischarge between the grid 4 and the grid 3, and the tube will thus stayin a non-conducting state when the condenser II is fully charged. Thedischarge condenser I I, connected across the conventionally shown powersupply through the impedance I2 in the manner before described, is usedfor high-frequency operation of the strobescope circuit; forlow-frequency operation, a condenser I3 is connected in parallel withthe condenser by means of aswitch 66.

Current is also supplied from the power supply to the conductors I00 andI32. The conductor I32 is connected, through a resistor I28, to a switch88, adapted .to occupy two positions A and B. The conductor I88 isconnected, by a contactor device 81, to a contact member with which theswitch 88 is adapted-to contact in position B. The circuits of thehereinafter-described multivibrator are open when the switch 88 occupiesthe position B. The (switch 86 is connected by a conductor 58, through acondenser 83. to the grid 3. The switch 86 is connected also to thealternating current, by way of a conductor 20, and through a resistor84, by a switch 85. The contactor 81 may be periodically opened andclosed in any-desired manner; this is not shown in order to simplify thedrawings.

The lamp circuit comprises the said two discharge condensers II and I3,the said currentlimiting resistor I2 and the three resistors 8|, 88,

With the switch 88 in position B, and the switch 88 open,'the' lamp Ican be triggered at the desired instant by means of the contactor device81, which causes a momentary surge through the condenser 83. When thecontactor device 81 closes, therefore, the grid '3 is given a negativevoltage pulse equal to the yoltag'e existing between the conductors I08and I32. The condenser'83 then discharges through the resistor 8| andthe grid 3 to the cathode 2, allowing-the voltage of the grid 3'toreturn to zero. The discharge circuit extends from one side of thecondenser 83, through theresistor 8| and the grid 3 and the cathode 2,in parallel, by way of the conductors 8, and I00, and through theswitches 81 and 86, the latter in the position B, to the other side ofthe condenser 83. Once the contactor 81 becomes closed, it may remainclosed without the stroboscope flashing on again when the condensers IIand I3 build up their voltages. The operation is independent of thelength of time that the contactor 81 remains closed, the completefunction being performed at the moment it first becomes closed.The-contactor 81, therefore, gives only one impulse of voltage at eachclosing, and the length of time the contactor 81 remains closed does notaffect the operation of the tube.

The negative voltage pulse applied to the grid- 3 starts a glowdischarge between the grid 3 and the grid 4, causing the tube I tobecome conducting, as described in connection with Fig. 3. This permitscondenser II or I3 (or both) to discharge through the tube, giving abrilliant flash of light, lasting but a few microseconds. The tube thenextinguishes and the condensers II and I8 recharge.

This process of charging the condenser II from the source of energy, anddischarging it through the vapor of the tube I, is repeated many times asecond, in synchronism with the opening and closing of the contactor 81.The use of the controlling oscillator, for impressing its oscillationsupon the grid 3, makes it possible to operate the stroboscope withoutany moving parts.-

The controlling oscillator for impressing its'oscillations upon the grid3 may be of any type, but the multi-vibrator oscillator is preferred,because of its simplicity, cheapness. constancy of frequencyirrespective of variations in applied voltage, abrupt wave form, and itscomparatively high voltage output.

The illustrated oscillator, therefore, is of the conventionalmulti-vibrator type, except for a novel method of controlling thefrequency, as will be hereinafter described. The direct-current powersupply for the oscillator is obtained from the power supply for thestroboscope circuit through the conductors 84 and 65 and the resistor81. A fllter condenser 88 is provided to remove any slightalternating-current ripple in the direct-current voltage.

The oscillator circuit comprises the vacuum triodes 88 and 89, the plateresistors or other impedances I22 and l24, the grid resistors I38 andI38 that are connected to the grids H4 and 8 of the triodes 89 and 88,the grid condensers I25, I28, I21 and I28, and the condenser I29. The

frequency-control circuit of the said oscillator comprises the variable,calibrating resistors or other impedances I2I and I38 and thepotentiometer H8. The set of electrodes of the vacuum triode 89,comprising the filament or cathode 98,

the grid H4 and the anode 92, and the set of electrodes of the vacuumtriode 88, comprising the filament or cathode 98, the grid H8 and theanode 94, may be in separate envelopes, or in a single envelope. It isusually more convenient to combine the two in a single tube. The voltagefrom the voltage source is applied to the oscillator by way oi theconductors I00 and I32, between which the oscillator is connected. Thecalibrating resistor I2I is connected between resistor 61 and conductorI32. The second calibrating resistor I30 is connected, in series withthe potentiometer IIO, to the conductor I 00. The potentiometer H8 isthus connected between the calibrating resistors I2I and I30. Thecathodes of the oscillator tubes, 88 and -89 are connected to theconductor I00. The anodes of the oscillator tubes are connected to theconductor I32 and the resistor I2I through the resistors I22 and I24.The switch isconnected, in position A, to the anode 94 of the triode 88.The anodes 92 and 94 are thus connected to one side of the source ofvoltage by the conductor I32, through the resistances I22 and I24. Thecathodes 96 and of these respective triodes are connected 0 to the otherside of the voltage source by the conductor I00. The slider I34 of thepotentlometer I I8 is connected to the two resistors or other impedancesI36 and I38 by a conductor I38.

The input circuit of the triode 89 may be traced from the filament 98,by way of the conductor I00, through the calibrating resistor I30, thelower portion of the potentiometer H8, and the adjustable arm I34, andby way of the conductor I33,'through the resistor I36, to the grid H4.The input circuit of the trlode 88 may similarly be traced from thefilament 98, by way of the conductor I00, through the calibratingresistor I30, the lower portion of the potentiometer H8, and theadjustable arm I34, and by way of the conductor I33, through theresistor I38, to the grid 8. The output circuit of the triode 89 may betraced from the filament 96, by way of the conductor I00, through thecalibrating resistor I30, the potentiometer H8, and the calibratingresistor l2! and, by way of the conductor I32, through the resistor I22,to the anode 92. The output circuit of the 'triode 88 may similarly betraced from the filament 98, by way of the conductor I 00, through thecalibrating resistor I30, the potentiometer H8 and the calibratingresistor I2I and, by way of the conductor I32. through the resistor I24,to the anode 94. The condenser I25 is connected between the grid H6 andthe anode 92, and the condenser I26 may be connected in paralleltherewith. The condenser I2! is similarly connected between the grid H4and the anode 94, and the condenser I28 may be connected in paralleltherewith.

With the switch 86 in the position A, the output of the oscillator,taken from the plate of one of the triodes, is connected to thestroboscopic lamp I through the coupling condenser 83 and the conductor58.

The principles of operation of the oscillator are well understood in theart and hence will not be gone into here.

As explained in a divisional application, Serial No. 167,618, filedOctober 6, 1937, to which reference may be made for further details, thefrequency may be controlled by adjusting the slider I24 back; and forthon the potentiometer H8 to vary the positive bias on the grids of thetriodes '08 and 09. This yields both a linear frequency conductor 20.This scale and a wide frequency range-as much as six to one. Thepotentiometer H8 is calibrated in flashes per minute of the stroboscopelamp,

, with the aid of a vibrating reed I40, driven by means of a solenoidI42, sistors I2I and I30.

To this end, the solenoid I42 is connected in circuit with a switch I44and conductors I46 and I48 across the alternating-current supply.

The said divisional application describes also an alternative method ofchecking the calibration by means of a glow lamp I50 and a resistor I49.

By closing the switch 85, an alternating-current voltage is applied tothe oscillator from transformer I8 through resistance 84 and the causesthe oscillator to run at the frequency of the line voltage and in exactsy'nchronism therewith. This is useful in certain applications of thestroboscope.

The light produced by this stroboscope, obtained from a -volt, 60-cyclealternatingcurrent source, is suflicient to permit good stroboscopicobservation of mechanisms, particularly when the light is concentratedby means of a parabolic reflector. Because of the calibrated frequencyscale, the stroboscope is particularly useful in measuring the speed ofrotating or vibrating mechanisms.

Further modifications will. occur to persons skilled in the art, and allsuch are considered to fall within the scope and spirit of theinvention.

What is claimed is: a

1. In an electric circuit, a gaseous-discharge tube comprising an anodeand a cold cathode of a material which will break down under the actionof a cathode spot and form a surface coating thereon of a material oflow wor -function, and means for subjecting the cathode and the and thecalibrating reode to cause destruction of the cathode by heat.

2. In an electric circuit, a gaseous-discharge tube comprising an anode,a cold cathode of a material which will break down under the action of acathode spot and form a surface coating amount to form a cathode spot onthe cathode but without supplying suflicient heat to the cathode tocause destruction of the cathode by heat. 3. In an electric circuit, agaseous-discharge tube comprising an anode, a cathode of a materialwhich will break down under the action of a cathode spot and form asurface coating thereon of a material of low work-function, a griddisposed between the anode and the cathand the first-named grid, andmeans for subjecting the cathode and the anode to energy suflicient incharacter and amount to form a cathode spot on the cathode but withoutsupplying suflicient heat to the cathode to cause destruction ofthecathode by heat.

4. In an electric circuit, a condenser arranged to be charged from asource of energy, a gaseousdischarge tube comprising an anode and a.cathode comprising a mixture of a caesium salt and a metal which willdisplace the caesium in the salt under the action of a cathode spot, theoathode being adapted to form a cathode spot thereon, and means forconnecting the condenser to the anode and the cathode to cause thecondenser to discharge through the tube to form a cathode spot on thecathode, I

5. In an electric circuit, a condenser arranged to be charged from asource of energy, a gaseousdischarge tube comprising an anode and acathode having a material from the group comprising the first and secondgroups of the periodic table of elements and the rareearths, the cathodebeing adapted to form a cathode spot thereon, andmeans for connectingthe condenser to the anode and the cathode to cause the condenser todischarge through the tube to form a cathode spot on the cathode.

6. An electric circuit having, in combination, a gaseous-dischargedevice comprising an envelope containing gas and having an anode and asolid cold cathode, the cathode being constituted of a material having arelatlvelylow work-function and that does not combine chemically withthe gas in the envelope, means for applying a voltage between the anodeand the cathode, and

means comprising the first-named means for passing an electricaldischarge between the anode and the cathode through the gas in theenvelope to produce a cathode spot on the cathode.

'1. An electric circuit having, in combination, a gaseous-dischargedevice comprising an envelope containing gas and having an anode and a.solid cold cathode, the cathode being constituted of a material having arelatively lowwork-function and that does not combine chemically withthe gas in the envelope, a condenser, means connecting the condenser tothe anode and t e oathode, means for periodically charging thecondenser, and means for periodically discharging the condenser betweenthe anode and the cathode to pass an electrical discharge between themthrough the gas in the envelope to produce a cathode spot on thecathode.

8. An electric circuit having, in combination, a gaseous-dischargedevice comprising an envelope containing gas and having an anode, asolid cold cathode, and a grid, the cathode being constituted of r amaterial having a relatively low work-function and that does not combinechemically with the gas in the envelope, an impedance connected betweenthe anode and the grid, a condenser, means connecting the condenser tothe anode and the cathode, means'for periodically charging thecondenser, and means for periodically discharging the condenser betweenthe anode and the cathode to pass an electrical discharge between themthrough the gas in the envelope to produce a cathode spot on thecathode.

9. An electric circuit having, in combination, a gaseous-dischargedevice comprising an envelope containing gas and having an anode, asolid cold cathode, and a grid, the cathode being constituted of amaterial having a relatively low work-function and that does not combinechemically with the gas in the envelope, an impedance connected betweenthe anode and the grid, an impedance connected between the cathode andthe grid, a condenser, means connecting the condenser to the anode andthe cathode in parallel to the impedances connected in series, means forperiodically charging the condenser, and means for periodicallydischarging the condenser between the anode and the cathode to pass anelectrical discharge between them through 'the gasin the envelope toproduce a cathode spot on the cathode.

10. An electric circuit having, in combination, a gaseous-dischargedevice comprising an envelope containing gas and having an anode, asolid lope containing cold cathode, a grid disposed between the anodeand the cathode, and'a grid disposed between the cathode and thefirst-named grid, the cathode being constituted of a material having arelatively low work-function and that does not combine chemically withthe gas in the envelope, an impedance connected between the anode andthe first-named grid, an impedance connected between the cathode and thefirst-named grid, a condenser, means connecting the condenser to theanode and the cathode in parallel to the impedances connected in series,an impedance con-' nected between the cathode and the secondnamed grid,means for periodically charging the condenser, and means forperiodically dischargingthe'condenser between the anode and the cathodeto pass an electrical discharge between" them through the gas in theenvelope to produce a. cathode spot on the cathode.

11. An electric "circuit having, in combination, a gaseous-dischargedevice comprising an envelope containing gas and having an anode, asolid cold cathode, and a grid, the cathode being constituted of amaterial having a relatively low workunction and that does not combinechemically with the gas in the envelope, an impedance connected betweenthe anode and the grid, a condenser, means connecting the condenser tothe anode and the cathode, means for periodically charging thecondenser, and means for periodically discharging the condenser betweenthe anode and the cathode to pass an electrical dis charge between themthrough the gas in the en'- velope to produce a cathode spot on thecathode, and the impedance being so proportioned that, when the voltageacross the condenser reaches a predetermined value, a discharge willtake place between the cathode and the grid and, therefore, between thecathode and the anode.

12. An electric circuit having, in combination, a gaseous-dischargedevice comprising an envelope containing gas and having electrodescomprising an anode and a solid cold cathode, the cathode beingconstituted of a material having a relatively low work-function and thatdoes not combine chemically with the gas in the envelope, means forapplying a voltage between the anode and the cathode, an oscillator, andmeans for impressing the oscillations of the oscillator upon one of theelectrodes to cause an electrical discharge to be passed between theanode and the cathode through the gas in the envelope to produce acathode spot on the cathode.

13. An electric circuit having, in combination,

a gaseous-discharge device comprising an enve- 5 gas and having ananode, a solid cold cathode, a grid disposedbetween the anode and thecathode, and a grid disposed between the cathode and the first-namedgrid, an impedance connected between the anode and the first-named grid,an impedance connected between the cathode and the first-named grid, acondenser, means connecting the condenser to the anode and the cathodein parallel to the impedances connected in series, an impedanceconnected between the cathode and the second-named grid, an oscillator,and means for impressing the oscillations of the oscillator upon thesecond-named grid to causedischarges to take place periodically betweenthe grids and, therefore, between the cathode and 76 cold cathode, and agrid, the cathode being con 15. In an electric circuit, agaseous-discharge tube comprising an anode, a cathode of a materialwhich will break down under the action of a cathode spot and form asurface coating thereon of a metal of low work-function, means forcausing a continuous glow discharge in the tube, a grid for preventingconduction between the anode and cathode, and means changing the bias onthe grid for causing an arc discharge between the anode and the cathode.

16. In an electric circuit, a gaseous-discharge tube comprising ananode, a cathode comprising a mixture of a caesium salt and a metalwhich will displace the caesium in the salt under the action of acathode spot and form a surface coating thereon of a metal of lowwork-function, means for causing a continuous glow discharge in thetube, a grid for preventing conduction between the anode and cathode,and means changing the bias on the grid for causing an are dischargebetween the anode and the cathode.

1'7. In an electric circuit, a gaseous-discharge tube comprising ananode, a caesium-containing cathode on which a cathode spot can beformed by a glow discharge to the cathode to form a surface coatingthereon of a metal of low workfunction, means for causing a continuousglow discharge in the tube, a grid for preventing conduction between theanode and cathode, and means changing the bias on the grid for causingan arc discharge between the anode and the cathode.

18. In an electric circuit, a gaseous-discharge tube comprising ananode, a cathode of a material which will break down under the action ofa cathode spot and form a surface coating thereon of a material of lowwork-function, a grid, and means causing a glow discharge to form acathode spot on the cathode.

19. In an electric circuit, a gaseous-discharge tube comprising ananode, a solid cathode on which a cathode spot can be formed by a glowdischarge, and means for continually but interruptedly passing currentbetween the anode and the cathode of amperage sufficiently high toproduce a potential gradient on a relatively small area only of thecathode high enough to extract electrons from the cathode while thecathode remains at low average temperature and to produce a fall ofcathode potential lower than that occurring to a glow discharge, andsufliciently low so that the root-mean-square value of this currentshall be low enough so that the average temperature applied thereby tothe cathode shall be less than the temperature at which substantiallyincandescent cathode emission is produced, thereby continually butinterruptedly to form a cathode spot on the cathode.

20. In an electric circuit, a gaseous-discharge tube comprising ananode, acathode of a material that will break down under the action of acathode spot and form a surface coating of a material of lowwork-function thereon, and means for continually but interruptedlypassing current between the anode and the cathode of amperagesuiilciently high to produce a potential gradient on a relatively smallarea only of the cathode high enouizh to extract electrons from thecathode while the cathode remains at low average temperature and toproduce a fall of cathode potential lower than that occurring in a glowdischarge, and sumcientiy low so that the rootmean-square value of thiscurrent shall be low enough so that the average temperature appliedthereby to the cathode shall be less than the temperature at whichsubstantially incandescent cathode emission is produced, therebycontinually but interruptedly to form a cathode spot on the cathode.

21. In an electric circuit, a gaseous-discharge tube haying .an anode, acathode comprising a mixture of a caesium salt and a metal which willdisplace the caesium in the salt under the action of a cathode spot, andmeans for continually but interruptedly passing current between theanode and the cathode of amperage sufllciently high to produce apotential gradient on a relatively small area only of the cathode highenough to extract electrons from the cathode while the cathode remainsat low average temperature and to produce a fall of cathode potentiallower than that. occurring in a glow dischargaand sumciently low so thatthe root-mean-square value of this current shall be low enough so thatthe average temperature applied thereby to the cathode shall be lessthan the temperature at which substantially incandescent cathodeemission is produced,

' thereby continually but interruptedly to form a cathode spot onthe.cathode.

22. In an electric circuit, a gaseous-discharge device comprising ananode, a solid cathode on which a cathode spot can be formed by a glowdischarge, means for continually setting up discharges of arccharacteristic between the cathode and the anode, and means forproviding intervals between the discharges sufliciently large so thatthe average temperature of the cathode shall below enough to preventrapid disintegration of the cathode, thereby continually butinterruptedly to form a cathode spot on the cathode.

23. In an electric circuit, a gaseous-discharge device comprising ananode, a cathode of a material that will break down under the action ofa cathode spot to form on the cathode a surface coating of a material oflow work-function, means for continually setting up discharges of arccharacteristic between the cathode and the anode, and means forproviding intervals between the discharges sufiiciently large so thatthe average temperature of the cathode shall be low enough to preventrapid disintegration of the cathode, thereby continually butinterruptedly to form a cathode spot on the cathode.

24. In an electric circuit, a gaseous-discharge device comprising ananode, a solid cathode on which a cathode spot can be formed by a glowdischarge, means for continually setting up discharges of arecharacteristic between the oathode and the anode, and means forproviding intervals between the discharges sufliciently large so thatthe average temperature of the cathode shall be less than thetemperature at which substantially incandescent cathode emission isproduced, thereby continually but interruptedly to form a cathode spoton the cathode.

'25. In an electric circuit, a gaseous-discharge device comprising ananode, a cathode comprising a first substance and also a compoundcontaining a second substance of a low work-function, the compound beinga material that will break down under the action of a cathode spot toform on terruptedly to form a cathode spot on the cath-.

ode.

26. In an electric circuit, a gaseous-discharge device comprising ananode, a caesium-containing cathode, means for continually setting updischarges of arc characteristic between the cathode and the anode, andmeans for providing intervals betwen the discharges sufilciently largeso that the average temperature of the cathode shall be low enough toprevent rapid disintegration of the cathode, thereby continually butinterruptedly to form a cathode spot on the cathode. I

27. In an electric circuit, a gaseous-discharge device comprising ananode, a barium-containing cathode, means for continuallysetting updischarges of arc characteristic between the cathode and the anode, andmeans for providing intervals between the discharges sufficiently largeso that the average temperature of the cathode shall be low enough toprevent rapid disintegration of the cathode, thereby continually butinterruptedly to form a cathode spot on the cathode.

28. In an electric circuit, a gaseous-discharge device comprising ananode, a cathode containing barium and a metal that wil displace thebarium under the action of a cathode spot, means for continually settingup discharges of arc characteristic betwen the cathode and the anode,and means for providing intervals between the discharges suflicientlylarge so that the average temperature of the cathode shal be low enoughto prevent rapid disintegration of the cathode, thereby continually butinterruptedly to form a cathode spot on the cathode.

29. In an electric circuit, a gaseous-discharge device comprising ananode, a cathode comprising a mixture of a caesium salt and a metal thatwill displace the caesium in the salt under the action of a cathodespot, means for continually setting up discharges of are characteristicbetween the cathode and the anode, and means for providing intervalsbetwen the discharges suiliciently large so that the average temperatureof the cathode shall be low enough to prevent rapid disintegration ofthe cathode, thereby continually but interruptedly to form a cathodespot on the cathode.

30. In an electric circuit, a gaseous-discharge dev e comprising ananode, a cathode comprising a mixture of a caesium salt and aluminum,means for continually setting up discharges of arc characteristicbetween the cathode and the anode, and means for providing intervalsbetween the discharges sufliciently large so that the averagetemperature of the cathode shall be low enough to prevent rapiddisintegration of the cathode, thereby continually but interruptedly toform a cathode spot on the cathode.

the cathode a surface coating oi the second substance, and the firstsubstance being amaterial 31. In an electric circuit, agaseous-discharge device comprising-an anode, a cathode comprising ,amixture of a caesium salt and cadmium, means for continually setting updischarges of arc characteristic between. the'cathode and the anode, andmeans for providing intervals between the discharges sufliciently largeso that the average temperature of the cathode shall be low enough toprevent rapid disintegration of the cathode,

thereby continually but interruptedly to form a cathode spot on thecathode.

32. In an electric circuit, a gaseous-discharge device comprising ananode, a cathode compris,

ing a mixture of caesium chloride and ametal that will displace thecaesium in the caesium chloride under the action of a cathode-spot,means for continually setting up discharges oi! are characteristicbetween the cathode and the anode, and means for providing intervalsbetween the discharges sufiiciently large so that the averagetemperature of the cathode shall be low enough to prevent rapiddisintegration of the cathode, thereby continually but interruptedly toform a cathode spot on the cathode.

33. In an electric circuit, a gaseous-discharge device comprising ananode, a cathode comprising a mixture of caesium'chloride and aluminum,means for continually setting up discharges of are characteristicbetween the cathode and the anode, and means for providingintervalsbetween the discharges sufiiciently large so that the averagetemperatureof the cathode shall be low enough to prevent rapid disintegration ofthe' device comprising an anode, a cathode comprising an open enclosureand a reactive mixture therein of a material that will break down underthe action of a cathode spot and form a surface coating thereon of amaterial of low work-function, means for continually setting updischarges of are characteristic between the cathode and the anode, andmeans for providing intervals between the discharges sufliciently largeso that the average temperature of thecathode shall be low enough toprevent rapid disintegration of the cathode, thereby continually butinterruptedly to form a cathode spot on the cathode.

35. In an electric circuit, a gaseous-discharge device comprising ananode, a cathode of a material that will break down under the action ofa cathode spot to form on the cathode a surface coating" of a materialof low work-function, means for continually'setting up discharges of arecharacteristic between the cathode and the anode, and means forproviding intervals between the discharges sufliciently large so thatthe average temperature of the cathode shall be low enough to preventrapid disintegration of the cathode, thereby continually butinterruptedly to form a cathode spot on the cathode, the device beingprovided with means for absorbing gaseous products that may result fromthe reaction of the cathode spot on the said material.

KENNETH J. GERMESHAUSEN.

